This invention relates to a gyroscope for detecting rotational angular velocity and, in particular, to a piezoelectric vibratory gyroscope comprising a piezoelectric vibrator vibrating in an energy-trapping vibration mode.
In the prior art, the gyroscope has often be used in direction sensors for car navigation systems and vibration sensors in image stabilizing systems for camcorders.
A piezoelectric vibratory gyroscope utilizes a mechanical phenomenon relating to Coriolis force. Specifically, when an object vibrating in a vibrating direction is subjected to a rotational angular velocity, the Coriolis force is produced in a direction perpendicular to the vibrating direction.
In a composite piezoelectric vibration system in which vibration can be excited in first and second directions perpendicular to each other, it is assumed that a piezoelectric vibrator is rotated while the vibration is excited in the first direction. In this event, the above-mentioned Coriolis force is produced in the second direction perpendicular to the first direction to excite the vibration in the second direction. By piezoelectric effect, the vibration in the second direction causes an electromotive force to produce an output voltage. It is noted here that the amplitude of the vibration in the second direction is proportional to an amplitude of the vibration in the first direction and the rotational angular velocity. If the amplitude of the vibration in the first direction is kept constant, the rotational angular velocity applied to the piezoelectric vibrator can be calculated from the output voltage.
A conventional structure of the piezoelectric vibratory gyroscope of a type described utilizes a bending vibration mode of the piezoelectric vibrator comprising a rectangular metal beam as a vibrating body and piezoelectric vibrating elements mounted on different surfaces of the vibrating body. The piezoelectric vibrator must be supported or fixed at nodal points of the vibration. Further, driving and detecting circuits must be connected to electrodes of the piezoelectric vibrating elements by the use of lead wires. Since the connection of lead wires affects the properties of the gyroscope, it is difficult to stably produce gyroscopes with constant characteristics. Furthermore, the piezoelectric vibrator must be supported by a holder and mounted on a substrate which is provided with the driving and detecting circuits thereon. With this structure, it is difficult to reduce the size and the thickness of the piezoelectric vibratory gyroscope.
On the other hand, a piezoelectric vibrator carrying out energy-trapping vibration is extensively used in an intermediate-frequency filter for a FM radio or a television. In the energy-trapping vibration, vibration energy is concentrated to the neighborhood of a driving electrode. The energy-trapping vibration includes various vibration modes such as extensional or shear vibration in either a thickness direction or a widthwise direction of a piezoelectric plate. It is noted here that the extensional vibration in the thickness direction is a vibration mode such that both the propagating direction of the vibration and the displacement by the vibration are parallel to the thickness direction of the piezoelectric plate. On the other hand, the shear vibration in the thickness direction is a vibration mode such that the propagating direction is parallel to the thickness direction while the displacement is perpendicular to the propagating direction. In the following, the latter may be briefly called the thickness-shear vibration. In the piezoelectric vibrator described above, a lead terminal can be formed at a desired position without being influenced by a support structure.
Accordingly, if the above-mentioned piezoelectric vibrator used in the intermediate-frequency filter can be applied to the piezoelectric vibratory gyroscope instead of the piezoelectric vibrator having the beam vibrating body, the above-mentioned disadvantages will be removed.